The present invention relates to power detectors. More specifically, it relates to a temperature-compensated power detector, which may be integrated into wireless communication devices. Examples of wireless communication devices include portable radio sets, mobile phones, Personal Digital Assistants (PDAs), wireless data-processing units, and the like.
For example, in a portable radio set, the output power level may vary with frequency, temperature and power supply. It may also vary from one portable radio set to another. The variations in the output power level may affect the performance of the portable radio set, or may disturb other radio sets operating in its proximity. Another example is a transmitter of a cellular base station employing the Global System for Mobile communication (GSM) standards, where variations exist in the output power level corresponding to different time slots. These variations have to be controlled.
Accordingly, a power detector is incorporated to detect the output power level of an RF signal, and control the variations in the output power level of the RF signal. The power detector detects the output power level of the RF signal and provides a voltage, which corresponds to that output power level. The voltage from the power detector is then used to control the output power level of the RF signal.
Generally, a power detector is designed with one or more diodes. A voltage across the junction of a diode is temperature-dependent. Consequently, the output voltage of the power detector is also temperature-dependent. This may limit the application of power detectors in electronic circuits, especially if variations in the output power level, as compared to the temperature, need to be tracked. Therefore, the output voltage of a power detector is made independent of the temperature by a process known as temperature compensation. A power detector with temperature compensation is referred to as a temperature-compensated power detector.
Various methods exist to temperature-compensate a power detector. In one such method, a balance (differential) amplifier is used. The output of a biased power detector diode is applied to one input of the balance (differential) amplifier, and the voltage from an identical DC-biased diode is applied to another input of the balance (differential) amplifier. If both the diodes have the same temperature dependence, the differential output voltage of the balance (differential) amplifier will be temperature-independent.
Another method utilizes a variable resistor arrangement, which is connected to the power detector as a load resistance. The load resistance is changed, either manually or automatically, along with the temperature, to temperature-compensate the power detector.
However, one or more of the methods to temperature-compensate a power detector needs elaborate circuitry, requiring space and power, to provide sufficient temperature compensation.
In light of the foregoing discussion, there is a need for a compact, low power-consuming temperature-compensated power detector. Moreover, the temperature-compensated power detector should have a good dynamic range and temperature stability.